U-tube steam generator with segment superheater

ABSTRACT

A steam generator having a U-shaped tube bundle utilized to transfer heat from a first fluid to second fluid feedwater, and having a dividing plate, which acts in conjunction with an arcuate plate to form a steam enclosure encompassing at least a portion of the hot leg of the tube bundle to provide a superheater portion, which cooperates with a preheater portion, disposed on the cold leg, and a boiler portion to produce superheated steam.

United States Patent [191 Lyman et a1.

[ UTUBE STEAM GENERATOR WITH SEGMENT SUPERHEATER [75] Inventors: WalterG. Lyman; Ted L.

Fetterman, both of Pittsburgh, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22; Filed: July 24,1972

21 Appl. No.: 274,695

[52] US. Cl. 122/32, 122/483 [51] F22b 1/06 [58] Field of Search 122/32,33, 34, 483

[ 56] References Cited UNITED STATES PATENTS 2,336,832 12/1943Badenhausen 122/34 2,922,404 l/1960 Kopp et a1 122/34 [4 1 Apr. 30, 19743,141,445 7/l964 Bell 122/34 3,209,731 10/1965 Schonberger et a1...3,267,907 8/1966 Glausser et a1. 122/483 X Primary Examiner-Kenneth W.Sprague Attorney, Agent, or FirmF. J. Baehr, Jr.

{57 ABSTRACT A steam generator han'ng a U-shaped tube bundle utilized totransfer heat from a first fluid to second fluid feedwater, and having adividing plate, which acts in conjunction with an arcuate plate to forma steam enclosure encompassing at least a portion of the hot leg of thetube bundle to provide a superheater portion, which cooperates with apreheater portion, disposed on the cold leg, and a boiler portion toproduce superheated steam.

7 Claims, 7 Drawing Figures Pal m 30 1914- IBEYLBS sum 1 0F 3PATENFEUAPR 30 m4 sum 2' 0F 3 U-TUBE STEAM GENERATOR WITH SEGMENTSUPERIIIEATER BACKGROUND OF THE INVENTION This invention relates tosteam generators for nuclear power plants and more particularly to suchsteam generators which produce superheated steam.

In order to improve the efficiency of a nuclear power plant utilizing apressurized water reactor, it is desirable to superheat the steamproduced by the steam generator. Once-through straight tube steamgenerators have been designed; however, the straight-through tubesintroduce problems, such as long hot leg pipes and the associatedaccident consideration, and manufacturing and stress problems due to thethermal expansion of the straight tubes.

U-tube steam generators which produce superheated steam and havedownflow boiling are expected to have problems with instability andmoisture carryover.

SUMMARY OF THE INVENTION In general, a steam generator when made inaccordance with this invention, utilizes a U-shaped tube bundle toprovide the heat transfer surface for transferring heat from a firstfluid to vaporize a second fluid. The tube bundle is so arranged thatthe first fluid flows through the tubes creating a hot leg portion and acold leg portion in the tube bundle. The steam generator has a tubesheet in which the ends of the tubes are fastened, a preheater portioncooperatively associated with the cold leg portion of the tube bundle,and a fluid inlet nozzle for the second fluid. The second fluid inletnozzle is disposed to introduce the second fluid into the preheaterportion, which has baffles and walls which cooperate to cause theinfluent second fluid to split and follow two sinuous paths over anouter portion of the heat transfer surface of the tubes forming the coldleg. One path is in a generally upward direction and the other path isin a generally downward direction and leaves the preheater in such amanner as to sweep the tube sheet before it flows upwardly in the steamgenerator. The portion of the cold leg cooperatively associated with thepreheater portion is limited to a predetermined heat transfer area,which will prevent vaporization of the second fluid until it isgenerally flowing in an upward direction in the steam generator.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of thisinvention will become more apparent from reading the following detaileddescription in connection with the accompanying drawings, in whichcorresponding reference characters indicate corresponding portions inthe various drawings and, in which:

FIG. I is a sectional view of a steam generator made in accordance withthis invention;

FIG. 2 is a sectional view taken on line IIII of FIG.

FIG. 3 is a sectional view of a second embodiment of a steam generatormade in accordance with this invention;

FIG. 4 is a sectional view taken on line III-III of FIG.

FIG. 5 is a sectional view of a steam generator made in accordance withthis invention;

FIG. 6 is a sectional view taken on line VIVI of FIG. 5; and

FIG. 7 is a sectional view taken on line VIIVII of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsin detail, FIGS. I and 2 show a vapor or steam generator I, whichutilizes U- shaped tubes 3 to form a tube bundle. which provides a heattransfer surface to transfer heat from a first fluid to vaporize or boila second fluid, generally water. The steam generator 1 comprises anelongated tubular shell 5, a tube sheet 7 in which the ends of the tubes3 are fastened, a channel head 9, which forms a header for the tubes 3,and a preheater 11. The channel head 9 is a hemispherical head having acentrally disposed dividing plate 13, which separates the inlet andoutlet portions 15 and 17, respectively. The inlet portion 15, theportion on the left as shown in FIG. 1, has an inlet nozzle 19 for theinfluent first fluid and the outlet portion 17 has an outlet nozzle 21for the effluent first fluid. The U-tubes 3 are so disposed that thefirst fluid flows from the inlet portion 15 of the head 9 through the U-shape tubes 3 and into the outlet portion 17 of the head 9 creating ahot leg 23, the one on the left in the drawings, and a cold leg 25, theone on the right in the drawings.

The preheater 11 is disposed on the lower end of the cold leg 25 andcomprises an enclosure having a top and bottom portion 26 and 27,respectively, and a flat and an arcuate plate 29 and 31, respectively,forming the side walls. The arcuate plate 31 extends from the lowerportion of a wrapper 32 which encompasses the tubes 3 and forms a spaceadjacent the shell 5 to protect it from thermal shocks. The shell 5 isexpanded outwardly adjacent the preheater I1 and a second fluid inletnozzle or feedwater nozzle 33 is disposed in the shell adjacent thereto.A thermal sleeve 35 is disposed in the inlet nozzle 33 and is incommunication with an inlet housing 37 disposed parallel to the arcuatewall 31 of the preheater II and directs the influent second fluid orfeedwater to the preheater. The thermal sleeve 35 and inlet housing 37cooperate to prevent the cold feedwater from contacting the inlet nozzle33 or the shell 5, in order to reduce thermal shocks and stressestherein.

A divider plate 39 extends upwardly from the tube sheet 7 parallel tothe tubes 3 and cooperates with the wrapper 32 to form a superheater orsteam enclosure 43 encompassing at least a portion of the hot leg 23 ofthe tube bundle. The steam enclosure 43 is in communication with asecondary fluid or steam outlet nozzle 45 through a steam outletenclosure 47, which directs the steam from the steam enclosure 43 to thesteam outlet nozzle 45. The dividing plate 39 is so disposed tocooperate with the tube bundle 3 and preheater 11 to vaporize or boilthe feedwater at such a rate that the second fluid entering the steamenclosure 43 is saturated steam or the quality is percent and theeffluent second fluid flowing through the outlet nozzle 45 issuperheated steam.

The steam or vapor generator shown in FIGS. 3 and 4 is similar to theone shown in FIGS. II and 2 except the steam outlet nozzle 45' isdisposed in the upper end of the vessel and the wrapper 32' encompassesthe tube bundle and forms an annular space between the shell 5 and thewrapper 32'. The annular space is utilized to allow steam to flow fromthe lower end of the steam enclosure 43 to the steam outlet nozzle 45 atthe top of the steam generator. The tube bundle 3 is also modified byomitting tubes adjacent the outer periphery to provide space for thefeedwater inlet and the shell 5' is not expanded outwardly adjacent thepreheater.

The steam or vapor generator shown in FIGS. 5, 6 and 7 is similar to theone shown in FIGS. 1 and 2 except the dividing plate 39" is rotated 90locating it in a plane parallel to a plane in which the U-shaped tubesare disposed so that preheater 11", evaporator and superheater 43"portions each contain both hot and cold leg portions of the U-shapedtubes.

The steam generators hereinbefore described advantageously utilizeU-shaped tubes to form a tube bundle, which is free to expand withvariation in temperature, and has a preheater portion, a boiler portionand a superheater portion cooperatively associated so that all boilingor vaporization takes place when the feedwater is flowing upwardly andsaturated vapor enters the superheater portion when the unit isoperating at rated load.

What is claimed is:

l. A vapor generator utilizing a U-shaped tube bundle to provide a heattransfer surface to transfer heat from a first fluid to vaporize andsuperheat a second fluid, said tube bundle being so arranged within saidvapor generator that said first fluid flows through said tubes creatinga hot leg portion and a cold leg portion in said tube bundle, said vaporgenerator comprising an elongated tubular shell, encompassing the tubebundle, a tube sheet in which the ends of the tubes are fastened, ahead, secured to said tube sheet and forming a header for the tubes, apreheater cooperatively associated with a portion of said cold leg, adivider plate disposed lengthwise in said shell said divider plateforming a portion of a vapor enclosure, a second fluid inlet nozzle incommunication with the preheater and a second fluid outlet nozzle incommunication with the vapor enclosure, whereby influent second fluidenters the preheater and is heated to a temperature below'itsvaporization temperature and then flows upwardly over a first majorportion of the heat transfer surface of the tube bundle changing stateof the second fluid from a liquid to a vapor and then the vapor entersthe vapor enclosure wherein it flows over a second major portion of theheat transfer surface of the tube bundle incorporating at least aportion of the hot leg, increases in temperature and becomes superheatedvapor prior to being discharged through the second fluid outlet nozzle.

2. A vapor generator as set forth in claim 1, wherein the vaporenclosure encompasses less than half of the tube bundle.

3. A vapor generator as set forth in claim 1, wherein the vaporenclosure encompasses a portion of the hot leg.

4. A vapor generator as set forth in claim 1, wherein the vaporenclosure comprises the dividing plate, a portion of a wrapper disposedto enwrap the tube bundle and an arcuate plate.

5. A vapor generator as set forth in claim 1, wherein the vaporenclosure, preheater and major portion of the tube bundle in whichvaporization takes place are cooperatively associated in such a mannerthat the vapor entering the vapor enclosure is at percent quality whenthere is rated load on the vapor generator.

6. A vapor generator as set forth in claim 1, and further comprising anenclosure disposed within the shell, said enclosure completelyenwrapping the tube bundle and providing an annular space between theenclosure and the shell in which the vapor flows .to the second fluidoutlet nozzle which is disposed in the upper end of the shell.

7. A vapor generator as set forth in claim 1, wherein the tubes areU-shaped and the dividing plate is disposed in a plane parallel toplanes in which the U- shaped tubes are disposed.

1. A vapor generator utilizing a U-shaped tube bundle to provide a heattransfer surface to transfer heat from a first fluid to vaporize andsuperheat a second fluid, said tube bundle being so arranged within saidvapor generator that said first fluid flows through said tubes creatinga hot leg portion and a cold leg portion in said tube bundle, said vaporgenerator comprising an elongated tubular shell, encompassing the tubebundle, a tube sheet in which the ends of the tubes are fastened, ahead, secured to said tube sheet and forming a header for the tubes, apreheater cooperatively associated with a portion of said cold leg, adivider plate disposed lengthwise in said shell said divider plateforming a portion of a vapor enclosure, a second fluid inlet nozzle incommunication with the preheater and a second fluid outlet nozzle incommunication with the vapor enclosure, whereby influent second fluidenters the preheater and is heated to a temperature below itsvaporization temperature and then flows upwardly over a first majorportion of the heat transfer surface of the tube bundle changing stateof the second fluid from a liquid to a vapor and then the vapor entersthe vapor enclosure wherein it flows over a second major portion of theheat transfer surface of the tube bundle incorporating at least aportion of the hot leg, increases in temperature and becomes superheatedvapor prior to being discharged through the second fluid outlet nozzle.2. A vapor generator as set forth in claim 1, wherein the vaporenclosure encompasses less than half of the tube bundle.
 3. A vaporgenerator as set forth in claim 1, wherein the vapor enclosureencompasses a portion of the hot leg.
 4. A vapor generator as set forthin claim 1, wherein the vapor enclosure comprises the dividing plate, aportion of a wrapper disposed to enwrap the tube bundle and an arcuateplate.
 5. A vapor generator as set forth in claim 1, wherein the vaporenclosure, preheater and major portion of the tube bundle in whichvaporization takes place are cooperatively associated in such a mannerthat the vapor entering the vapor enclosure is at 100 percent qualitywhen there is rated load on the vapor generator.
 6. A vapor generator asset forth in claim 1, and further comprising an enclosure disposedwithin the shell, said enclosure completely enwrapping the tube bundleand providing an annular space between the enclosure and the shell inwhich the vapor flows to the second fluid outlet nozzle which isdisposed in the upper end of the shell.
 7. A vapor generator as setforth in claim 1, wherein the tubes are U-shaped and the dividing plateis disposed in a plane parallel to planes in which the U-shaped tubesare disposed.